1. Field of the Invention
The present invention relates to a sidelight-type backlight apparatus for a liquid crystal display, and a liquid crystal display using the same.
2. Description of the Related Art
Recently, the reduction of thicknesses, sizes and weights of liquid crystal displays, the increases of their brightness and the savings of their power consumption have been demanded. In order to respond to these demands, a backlight apparatus using a light emitting diode (hereinafter, simply called an “LED”) as a light source, instead of using a fluorescent lamp, has been developed. A backlight apparatus using an LED as a light source can reduce its size and can save its power consumption because of its structure, compared with the case of using a fluorescent lamp. Moreover, the backlight apparatus does not contain mercury that is contained in a fluorescent lamp, and thus has excellent environmental friendliness. Thus, the backlight apparatuses using LEDs as the light sources are increasingly applied to liquid crystal displays that have small-sized screens for portable terminals such as mobile phones and PDAs, in particular.
As a representative example of the backlight apparatus using the LED as the light source, a sidelight-type backlight apparatus is known. See, for example, JP 11 (1999)-353920 A (Patent Document 1) and JP 2001-43717 A (Patent Document 2). FIG. 16 is a perspective view showing an example of a structure of a conventional sidelight-type backlight apparatus. Moreover, FIG. 17 is a perspective view showing another example of the structure of the conventional sidelight-type backlight apparatus.
As shown in FIG. 16, in the sidelight-type backlight apparatus, a plurality of channels are provided on one lateral face 53 of a light guide plate 51 such that an inside face of the channel serves as an incident face 54. Moreover, a main face on one side of the light guide plate 51 (an upper side in the figure) serves as a light exit face 55. In the example of FIG. 16, in order to suppress a brightness irregularity and a color irregularity of the display screen, a plurality of LEDs 52 are disposed as the light sources. The plurality of the LEDs 52 are arranged along a thickness direction of the light guide plate 51 and a direction perpendicular to the thickness direction, on the incident face 54 side of the light guide plate 51. An emitting direction of each LED 52 is directed to the incident face 54. It should be noted that a structure of the attachment of the LED 52 is not illustrated in FIG. 16.
Moreover, on a lateral face on which the incident face 54 is not provided and on a main face opposed to the light exit face 55, a reflection plate or a reflection sticker is attached, which is not illustrated in FIG. 16. Thus, emitting light from the LED 52 is incident from the incident face 54 to an inside of the light guide plate 51, repeats reflection inside the light guide plate 51, and thereafter, exits from the light exit face 55 of the light guide plate 51.
As a structure of arranging the plurality of the LEDs, a structure using a substrate shown in FIG. 17 is known. See, for example, JP 2002-75038 A (Patent Document 3). As shown in FIG. 17, on the substrate 56, the plurality of the LEDs 52 for irradiating with light toward a normal line direction of a substrate face are mounted. This substrate 56 on which the LEDs 52 are mounted is disposed so as to be parallel with the lateral face 53 of the light guide plate 51. According to this structure, the plurality of the LEDs 52 can be arranged easily.
The backlight using such LEDs as the light sources can contribute to the reductions of a thickness and a weight of a liquid crystal display, the use of less mercury (environmental friendliness) because of not using a fluorescent lamp, and the saving of the power consumption. Thus, the application of the backlight apparatus to liquid crystal displays that have large-sized screens, for example, liquid crystal monitors for personal computers and liquid crystal televisions is also expected in the future.
By the way, in the light guide plate constituting the backlight apparatus, the main face (the light exit face) is required to have a larger area, as the screen size of the liquid crystal display is larger. Whereas, in the light of the reduction of the thickness of the liquid crystal display, an increase of a thickness (an area of the lateral face) of the light guide plate is required to be suppressed as much as possible.
Accordingly, a ratio of the area of the lateral face of the light guide plate with respect to the display area of the liquid crystal display is decreased, as the screen size of the liquid crystal display is increased, and as a result, a ratio of a mounting area of the substrate for mounting the LED with respect to the display area is also decreased, as the screen size of the liquid crystal display is increased. Moreover, an amount of light that can be emitted by one LED is limited. Thus, in order to secure sufficient brightness by using the backlight apparatus having the LED as the light source in a liquid crystal display that has a large-sized screen, a mounting density of the LEDs to be mounted on the substrate is required to be higher, as the area of the main face of the light guide plate in the backlight is a larger.
However, for example, in the example of FIG. 17, a pitch between the LEDs 52 to be mounted on the substrate 56 is limited by a function of a mounter and securing of a soldering region. Moreover, even when the plurality of the LEDs 52 are arranged and mounted also in the thickness direction of the light guide plate 51 so as to increase the number of the LEDs 52 as shown in FIG. 16, a pitch between the LEDs 52 that are adjacent in the thickness direction is also limited similarly to the above-described case.
Because of these reasons, the mounting density of the LEDs 52 that can be mounted on the substrate 56 has a limitation. Thus, in the case where the sidelight-type backlight apparatus that has the conventional LEDs as the light sources is applied to a liquid crystal display that has a large-sized screen, it is extremely difficult to secure sufficient brightness.